Article in press; The degradation of titanium-based oral rehabilitation systems can occur by corrosion and wear processes taking place simultaneously (tribocorrosion) and influenced by the presence of fluorides. In this study, the tribocorrosion behavior of titanium in artificial saliva solutions containing fluorides is investigated. Before sliding tests were started up, electrochemical measurements such as open circuit potential (OCP) and impedance spectroscopy (EIS) were performed to get information on the corrosion behavior of titanium in artificial saliva solutions. Then, sliding wear tests were carried out at the OCP taken by the test sample. Scanning electron microscopy and weight loss measurements were performed after the tribocorrosion tests.
The presence of a compact passive surface film on titanium immersed was demonstrated in artificial saliva free of fluorides and in presence of up to 227 ppm F-. However, a progressive degradation of titanium was observed at a F- concentration of 12,300 ppm. Additionally, the corrosion and wear resistance of the titanium oxide film formed at a F- concentration of 12,300 ppm differ from the ones obtained up to 227 ppm F- reflected by a decrease of the coefficient of friction although the material loss increased. The synergism between wear and corrosion processes on titanium needs thus to be further investigated to reach a reliable prediction of the long-term behavior of titanium-based prostheses and implants in the oral cavity.

Impurity-interstitial dipoles in calcium fluoride solutions with Al3+, Yb3+ and La3+ fluorides were studied using the thermally stimulated depolarization current (TSDC) technique. The dipolar complexes are formed by substitutional trivalent ions in Ca2+ sites and interstitial fluorine in nearest neighbor sites. The relaxations observed at 150 K are assigned to dipoles nnR(S)(3+)- F-i(-) (R-S = La or Yb). The purpose of this work is to study the processes of energy storage in the fluorides following X-ray and gamma irradiation. Computer modelling techniques are used to obtain the formation energy of dipole defects. (C) 2007 Elsevier Ltd. All rights reserved.

Since the early findings on the protective effects of fluoride present in drinking water upon caries incidence and prevalence, intensive research has been conducted in order to determine the benefits, safety, as well as the cost-effectiveness of other modalities of fluoride delivery. The present chapter reviews the various forms of topical fluoride use - professionally and self-applied - with special emphasis on clinical efficacy and possible side effects. The most widely used forms of fluoride delivery have been subject of several systematic reviews, providing strong evidence supporting the use of dentifrices, gels, varnishes and mouth rinses for the control of caries progression. Dentifrices with fluoride concentrations of 1,000 ppm and above have been shown to be clinically effective in caries prevention when compared to a placebo treatment, but the evidence regarding formulations with 450-550 ppm is still subject of debate. Therefore, the recommendation for low-fluoride dentifrice use must take into account both risks and benefits. The evidence for the combined use of two modalities of fluoride application in comparison to a single modality is still inconsistent, implying that more studies with adequate methodology are needed to determine the real benefits of each method. Considering the currently available evidence and risk-benefit aspects...

Concerns about the quality of groundwater have been continuously rising, considering its importance for the public water supply in the State of São Paulo, and even more due to the impact that anthropic action has been causing to the original quality of that natural resource. It is extremely relevant to identify the contamination focuses along the aquifers of the State of São Paulo. This report aims to evaluate nitrates and fluorides concentrations along the aquifers present in the state, in order to identify places where change in the quality of groundwater is observed, through the comparison between measured concentrations and reference values, such as: “Intervention Value” (maximum allowed value) and “Alert Value” (attention required value). To perform this research, a full compilation and organization has been done on chemical analysis data from the “Sistema de Informações de Águas Subterrâneas - SIDAS”, made available by the “Divisão de Procedimentos de Outorga – DPO” of the “Departamento de Água e Energia Elétrica – DAEE”. This work has made possible the build-up of a database composed by 6,860 wells, with analytical data ready to be interpreted, containing information about water pH, electrical conductivity...

2-Deoxy-2-fluoro-beta-glucosyl and -beta-mannosyl fluorides administered to rats in a single dose (10 mg/kg) inhibited beta-glucosidase and beta-mannosidase activity respectively after 1 h in brain, spleen, liver and kidney tissues. This inhibition, presumably caused by accumulation of 2-deoxy-2-fluoroglycosyl-enzyme intermediates, indicates that intact 2-deoxy-2-fluoroglycosyl fluorides are distributed to these organs and, in the case of brain, that they cross the blood/brain barrier. beta-Glucosidase activity recovered completely or partially in brain, spleen, liver and kidney by 20-48 h. beta-Mannosidase activity partially recovered in all tissues by 48 h. beta-Galactosidase activity in brain and kidney was not significantly affected by administration of either the gluco or manno compounds at this dosage, indicating that these inhibitors are directed towards specific glycosidases. Observation of similar relatively rapid rates of beta-glycosidase re-activation in vivo and in tissue homogenates in vitro at 37 degrees C suggests that hydrolysis or transglycosylation of 2-deoxy-2-fluoroglycosyl-enzymes, not protein synthesis, are the primary mechanisms involved in the recovery of glycosidase activity inhibited by this class of compounds in vivo.

The enzymic hydrolysis of glycosyl fluorides is conveniently followed by using a pH-stat. Reactions involving glucosyl or galactosyl fluorides can also be followed by using glucose oxidase or galactose oxidase respectively. The pH-stat allows the rapid assay of intestinal α-glucosidase in crude homogenates. Use of glycosyl fluorides as substrates for glycosidases facilitates the polarimetric or g.l.c. determination of the anomeric nature of the initial product of hydrolysis. Hydrolysis by fungal amyloglucosidase proceeds with inversion of configuration whereas that by yeast and rat intestinal α-glucosidase, coffee-bean α-galactosidase and almond emulsin β-glucosidase proceeds with retention of configuration. β-d-Glucopyranosyl azide was not a detectable substrate for almond emulsin β-d-glucosidase.

Molecules that bind selectively to a given protein and then undergo a rapid chemoselective reaction to form a covalent conjugate have utility in drug development. Herein a library of 1,3,4-oxadiazoles substituted at the 2 position with an aryl sulfonyl fluoride and at the 5 position with a substituted aryl known to have high affinity for the inner thyroxine binding subsite of transthyretin (TTR) were conceived of by structure-based design principles and were chemically synthesized. When bound in the thyroxine binding site, most of the aryl sulfonyl fluorides react rapidly and chemoselectively with the pKa-perturbed K15 residue, kinetically stabilizing TTR and thus preventing amyloid fibril formation, known to cause polyneuropathy. Conjugation t50s range from 1 to 4 min, ~ 1400 times faster than the hydrolysis reaction outside the thyroxine binding site. X-ray crystallography confirms the anticipated binding orientation and sheds light on the sulfonyl fluoride activation leading to the sulfonamide linkage to TTR. A few of the aryl sulfonyl fluorides efficiently form conjugates with TTR in plasma. A few of the TTR covalent kinetic stabilizers synthesized exhibit fluorescence upon conjugation and therefore could have imaging applications as a consequence of the environment sensitive fluorescence of the chromophore.

Activation of the C–F bond of benzylic fluorides was achieved using 1,1,1-tris(hydroxymethyl)propane (2) as a hydrogen bond-donating agent. Investigations demonstrated that hydrogen bond-donating solvents are promoting the activation and hydrogen bond-accepting ones are hindering it. However, the reaction is best run under highly concentrated conditions, where solvents cannot interfere with the interaction between the organofluorine compound and the triol. Various benzylic fluorides react with secondary amines or anilines to form benzylic amines in good yields.

Transition metal fluorides are an appealing alternative to conventional intercalation compounds for use as cathodes in next-generation lithium batteries due to their extremely high capacity (3–4 times greater than the current state-of-the-art). However, issues related to reversibility, energy efficiency and kinetics prevent their practical application. Here we report on the synthesis, structural and electrochemical properties of ternary metal fluorides (M1yM21-yFx: M1, M2=Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid–solution CuyFe1-yF2, reversible Cu and Fe redox reactions are achieved with surprisingly small hysteresis (<150 mV). This finding indicates that cation substitution may provide a new avenue for tailoring key electrochemical properties of conversion electrodes. Although the reversible capacity of Cu conversion fades rapidly, likely due to Cu+ dissolution, the low hysteresis and high energy suggest that a Cu-based fluoride cathode remains an intriguing candidate for rechargeable lithium batteries.

Background: There are many forms of topical fluoride available today, making the decision as to which is most effective to manage the immediate caries risk problem at hand, very difficult. The objective of this project was to determine the concentration and pattern of fluoride ion uptake into enamel from a variety of categories of topical fluoride recently available in Australia. Methods: Extracted, intact molar teeth were sectioned to provide six plates of smooth surface enamel. Windows of enamel 2 x 6mm were exposed to a variety of topical fluorides for periods simulating those used in vivo. Following drying, the slates of enamel were exposed to 2ml of 0.1M HCl as a chemical biopsy agent for incremental periods of time. The concentrations of fluoride ion in the biopsy solutions for both test and background (control) slates of enamel were determined directly using a fluoride combination selective electrode in conjunction with a high impedance pH meter. Cumulative amounts of fluoride were determined for each topical fluoride agent. Results: The concentrations of fluoride ion taken up into enamel were generally proportional to those present in each agent. However, those from APF gel greatly exceeded the amounts taken up from NaF gel. Also...

Various solid-solid, solid-gas, and gas-gas reactions were explored for preparation of new refractory metal-nitrogen-fluorine compounds. The gas-gas reactions represent a new method for preparing this type of compound.
The reaction of metal fluoride vapors with ammonia yielded two new nitride-fluorides, Y(,2)NF(,3) and TiNF, as confirmed by electron microprobe analysis and x-ray powder diffraction. Using computer methods in indexing x-ray powder patterns, crystal systems were found for both. Y(,2)NF(,3) crystallizes with nearly the same hexagonal unit cell as TcNF giving lattice constants of a(,0) = 5.93 (ANGSTROM) and c(,0) = 4.79 (ANGSTROM). TiNF was indexed with a low-symmetry triclinic unit cell, a(,0) = 9.76 (ANGSTROM), b(,0) = 5.88 (ANGSTROM), c(,0) = 5.47 (ANGSTROM), (alpha)(,0) = 77.52(DEGREES), (beta)(,0) = 136.24(DEGREES), (gamma)(,0) = 112.27(DEGREES). Evidence for the formation of Sc(,2)NF(,3) and Al(,2)NF(,3) is also presented. These compounds are amorphous but give elemental analyses consistent with theoretical percentages.
Calculations of estimated heats of formation for nitride-fluorides have been made, assuming ionic crystals and using the Kapustinsky approximation, the third electron affinity of nitrogen, and other physical and thermodynamic data for the components in Born-Haber cycle relationships. These results confirm the refractory nature of the nitride-fluorides and their resistance to attack by HF and F(...

Main objectives of the thesis are: i. to verify a sealed chamber acid digestion technique for dissolution of plant material for total F analysis by a F ion selective electrode.--ii. to improve this technique for routine, rapid F analysis of plant material.--iii. to identify the inorganic ionic species of F which could be present in the soil solution.--iv. to determine which of these species are taken up by the plant root and those which are toxic to the plant.; Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1996; Copies of author's previously published articles in pocket.; Bibliography: leaves 203-219.; xv, 219 leaves : ill. ; 30 cm.; Title page, contents and abstract only. The complete thesis in print form is available from the University Library.

Fluoroform (HCF3, HFC-23) is a side product in the manufacture of polytetrafluoroethylene (Teflon). Despite its attractive properties, taming HCF3 for trifluoromethylation is quite problematic owing to its low acidity and the lability of the naked trifluoromethyl carbanion generated from HCF3. Herein we report the organic-superbase-catalyzed trifluoromethylation of ketones and arylsulfonyl fluorides by HCF3. The reactions were carried out by using a newly developed “superbase organocatalyst system” consisting of catalytic amounts of P4-tBu and N(SiMe3)3. A series of aryl and alkyl ketones were converted into the corresponding α-trifluoromethyl carbinols in good yields under the organocatalysis conditions in THF. The superbase organocatalytic system can also be applied to the trifluoromethylation of arylsulfonyl fluorides for biologically important aryl triflones in THF or DMF in good yields. Protonated P4-tBu, H[P4-tBu]+, is suggested to be crucial for the catalytic process. This new catalytic methodology using HCF3 is expected to expand the range of synthetic applications of trifluoromethylation.

In three quarters of a century of observation and research, the effects of fluoride on dental caries and on general bodily health have been well documented. An expanding data base has allowed a firming up of the guidance and standards for appropriate and safe levels of naturally occurring fluorides for human consumption. Over time, through specific recommendations, the maximum fluoride concentrations deemed appropriate have been altered, but by a process of considered adjustment. Although the Public Health Service has been responsible for the formalization of many of the recommended standards, those recommendations have been based on research from many fronts. In the most recent reconsideration of the standards for natural fluoride, the most exhaustive and thoroughly documented review to date was done, incorporating review by representatives from State, Federal, and private programs. Although the specific example of the development of standards for natural fluoride is used, it should be illustrative of similar processes that are constantly underway in regard to substances and factors with a potential impact on the public's health. Expansion of the data base through research and scientific inquiry will lay the foundation for future reconsideration of the standards for naturally occurring fluorides.

We present a first principles study of the series of multiferroic barium
fluorides with the composition BaMF4, where M is Mn, Fe, Co, or Ni. We discuss
trends in the structural, electronic, and magnetic properties, and we show that
the ferroelectricity in these systems results from the "freezing in" of a
single unstable polar phonon mode. In contrast to the case of the standard
perovskite ferroelectrics, this structural distortion is not accompanied by
charge transfer between cations and anions. Thus, the ferroelectric instability
in the multiferroic barium fluorides arises solely due to size effects and the
special geometrical constraints of the underlying crystal structure.; Comment: 8 pages, 6 figures, 3 tables

The catalytic asymmetric synthesis of alkyl fluorides, particularly α-fluorocarbonyl compounds, has been the focus of substantial effort in recent years. While significant progress has been described in the formation of enantioenriched secondary alkyl fluorides, advances in the generation of tertiary alkyl fluorides have been more limited. Here, we describe a method for the catalytic asymmetric coupling of aryl alkyl ketenes with commercially available N-fluorodibenzenesulfonimide (NFSI) and C_6F_5ONa to furnish tertiary α-fluoroesters. Mechanistic studies are consistent with the hypothesis that the addition of an external nucleophile (C_6F_5ONa) is critical for turnover, releasing the catalyst (PPY*) from an N-acylated intermediate. The available data can be explained by a reaction pathway wherein the enantioselectivity is determined in the turnover-limiting transfer of fluorine from NFSI to a chiral enolate derived from the addition of PPY* to the ketene. The structure and the reactivity of the product of this proposed elementary step, an α-fluoro-N-acylpyridinium salt, have been examined.

The catalytic asymmetric synthesis of alkyl fluorides, particularly α-fluorocarbonyl compounds, has been the focus of substantial effort in recent years. While significant progress has been described in the formation of enantioenriched secondary alkyl fluorides, advances in the generation of tertiary alkyl fluorides have been more limited. Here, we describe a method for the catalytic asymmetric coupling of aryl alkyl ketenes with commercially available N-fluorodibenzenesulfonimide (NFSI) and C_6F_5ONa to furnish tertiary α-fluoroesters. Mechanistic studies are consistent with the hypothesis that the addition of an external nucleophile (C_6F_5ONa) is critical for turnover, releasing the catalyst (PPY*) from an N-acylated intermediate. The available data can be explained by a reaction pathway wherein the enantioselectivity is determined in the turnover-limiting transfer of fluorine from NFSI to a chiral enolate derived from the addition of PPY* to the ketene. The structure and the reactivity of the product of this proposed elementary step, an α-fluoro-N-acylpyridinium salt, have been examined.

The objective of this work is to find a suitable correlation that best fits the specific heat of metals, metal oxides and metal fluorides as a function of temperature. It was found that a multilinear regression model of the form C P = aTb e cTe d/T has the lowest deviation from experimental data compared to other correlations including a 4th to 6th-order polynomial regression model. The coefficient of determination, R², was very close to unity in most cases and the average of the absolute relative errors, AARE, was less than 5% for the specific heat of most of the systems studied. The overall AARE was about 1.8% for metals and 3% for metal oxides and metal fluorides, which is within the experimental error.

Dental caries remain a public health problem for many developing countries and for underprivileged populations in developed countries. This paper outlines the historical development of public health approaches to the use of fluoride and comments on their effectiveness. Early research and development was concerned with waterborne fluorides, both naturally occurring and added, and their effects on the prevalence and incidence of dental caries and dental fluorosis. In the latter half of the 20th century, the focus of research was on fluoride toothpastes and mouth rinses. More recently, systematic reviews summarizing these extensive databases have indicated that water fluoridation and fluoride toothpastes both substantially reduce the prevalence and incidence of dental caries. We present four case studies that illustrate the use of fluoride in modern public health practice, focusing on: recent water fluoridation schemes in California, USA; salt fluoridation in Jamaica; milk fluoridation in Chile; and the development of "affordable" fluoride toothpastes in Indonesia. Common themes are the concern to reduce demands for compliance with fluoride regimes that rely upon action by individuals and their families, and the issue of cost. We recommend that a community should use no more than one systemic fluoride (i.e. water or salt or milk fluoridation) combined with the use of fluoride toothpastes...